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European Journal of Heart Failure 2006 8(4):361-365; doi:10.1016/j.ejheart.2005.10.008
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© 2006 European Society of Cardiology

Vasoactive intestinal peptide—release from the heart and response in heart failure due to left ventricular pressure overload

Markku Kuparia,*, Tomi S. Mikkolab, Heikki Turtoa, Jyri Lommia and Olavi Ylikorkalab

a Division of Cardiology, Department of Medicine, Helsinki University Central Hospital 00029 Helsinki, Finland
b Department of Obstetrics and Gynecology, Helsinki University Central Hospital 00029 Helsinki, Finland

* Corresponding author. Tel.: +358 9 47172441; fax: +358 9 47174574. E-mail address: markku.kupari{at}hus.fi


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 
Background: Vasoactive intestinal peptide (VIP) is a peptidergic neurotransmitter and a vasodilator with positive inotropic and chronotropic properties. Whether and how VIP contributes to the neuroendocrine response in heart failure (HF) is disputed, and there are no data on VIP in pressure overload-induced HF.

Methods: We studied 129 adults with isolated aortic valve stenosis (AS). Blood was sampled from the aortic root and, in a subset of 48 patients, also from the coronary sinus for determination of VIP by radioimmunoassay. HF was diagnosed according to the European Society of Cardiology criteria.

Results: Plasma VIP (mean±S.E.M.) was slightly higher in patients with HF (22.6±0.9 pmol/l, n=41) than in patients free of HF (21.1±0.5 pmol/l, n=88) or in 11 control patients without structural heart disease (20.0±1.3 pmol/l, n=11) (p=0.030 across the groups). VIP did not correlate with any measurement of cardiac structure or function in AS. The change in plasma VIP from aortic root to coronary sinus averaged +1.2±0.4 pmol/l in the 11 control patients (p=0.021), +1.2±0.2 pmol/l in 33 AS patients free of HF (p<0.001) and +0.8±0.3 pmol/l in 15 AS patients with HF (p=0.037).

Conclusions: Both structurally normal and diseased hearts release VIP into the coronary sinus. Although marginally elevated in the systemic circulation, VIP is unlikely to contribute significantly to the neuroendocrine activation in HF due to pressure overload.

Key Words: Heart failure • Aortic stenosis • Vasoactive intestinal peptide

Received March 13, 2005; Revised July 30, 2005; Accepted October 11, 2005


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 References
 
Vasoactive intestinal peptide (VIP) is a peptidergic neurotransmitter, first identified in the intestines but later found in many other organs as well, including the heart, arteries and veins [1]. Synthesized in postganglionic neurons, or in intrinsic neurons involved in local reflexes, and released from presynaptic nerve terminals, VIP activates specific receptors stimulating adenylyl cyclase and cAMP production [1-3]. Both animal and human studies have shown that VIP is a powerful systemic and pulmonary vasodilator and possesses positive inotropic and chronotropic properties [1]. It also dilates epicardial coronary arteries, reduces coronary vascular resistance and is cardioprotective during acute experimental myocardial ischaemia [1,4,5]. As an endogenous inodilator, VIP could contribute to the counter regulatory neurohumoral activation in heart failure (HF). Although there are small studies showing elevated circulating VIP in HF [6,7], other studies have given negative [8,9] or mixed findings [10]. We set out to clarify this issue by studying the circulating concentrations and the cardiac release of VIP in HF due to left ventricular (LV) pressure overload. We measured aortic and coronary sinus VIP concentrations in patients with and without HF due to aortic valve stenosis (AS) and in control patients free of structural heart disease.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 References
 
2.1. Patients and study protocol
We studied 129 patients (64 men) with AS referred to us for consideration for valve replacement. The mean age (±S.D.) was 69±10 years (range, 39-83). The patients constituted a consecutive series except that we excluded individuals with history of myocardial infarction, more than mild aortic regurgitation, more than mild mitral valve disease, previous cardiac surgery, complicated diabetes and renal failure (serum creatinine >170 µmol/l). Eight patients were asymptomatic while 76, 43 and 2 patients were in New York Heart Association (NYHA) classes 2, 3 and 4, respectively. Eleven patients had chronic atrial fibrillation. At the time of our study, 80 patients were on beta-adrenergic blockers, 48 on diuretics, 29 on angiotensin-converting enzyme inhibitors, 20 on long-acting nitrates and 9 on digoxin.

All patients underwent clinical assessment, 6-min walk test, echocardiography and a complete cardiac catheterization with sampling of blood for laboratory analyses. In addition to VIP, we determined plasma NT-proBNP and endothelin-1 as reference endogenous vasoactive agents involved in the neuroendocrine response to HF. VIP and other peptides were also measured in a control group of 11 patients (6 men) undergoing invasive electrophysiological studies for paroxysmal supra-ventricular tachyarrhythmias (n=10) or syncope (n=1). Their mean age was 57±4 years. No control patient had symptoms or signs of cardiac disease aside from the history of arrhythmias, and all had sinus rhythm and normal echocardiograms at the time of our study.

Our investigation conforms with the principles outlined in the Declaration of Helsinki and was approved by the ethics committee of our institution. All participants signed an informed consent document.

2.2. Non-invasive and invasive cardiac studies
Echocardiographic studies were done with an Acuson Sequoia scanner. The details and reproducibility of the methods used have been reported earlier [10,11]. Left ventricular (LV) mass index (mass/body area) was calculated from 2-dimensionally guided M-mode recordings using an anatomically validated method [12]. Ejection fraction was determined from the apical 4-chamber view using Simpson's formula (n=123) or from the parasternal M-mode measurements by the Teicholz equation (n=6).

Cardiac catheterizations were scheduled in the morning following an overnight fast. The patients were mildly sedated and they received their regular medication except that the day's first dose of diuretic was omitted. Pressures in the right and left heart were determined using fluid-filled catheters with zero reference level at the mid-axillary line. Cardiac output was measured using the Fick technique. The aortic valve area was calculated by the Gorlin formula and indexed to body area. If the aortic valve could not be crossed retrograde (n=13), echocardiographic valve area was used instead. Coronary angiography was performed using standard selective techniques and analyzed visually. Luminal reductions exceeding 50% of the reference diameter were considered to represent angiographically significant coronary artery disease.

HF was diagnosed when the patient had dyspnoea or fatigue on ordinary effort, associated with resting pulmonary wedge pressure >14 mm Hg at cardiac catheterization [13]. HF was classified as diastolic if the LV ejection fraction was ≥50% and systolic if the ejection fraction was <50%.

2.3. Blood sampling and laboratory analyses
Blood for VIP and other analyses was drawn from the aortic root and the coronary sinus before LV catheterization or angiography in patients with AS and at the beginning of the electrophysiological study in the control group. The samples were taken into prechilled EDTA tubes containing aprotinin, put immediately on ice and centrifuged within 20-30 min. Plasma was stored at –80 °C prior to analysis. The coronary sinus was accessible for blood sampling in all control patients and in a subset of 48 patients with AS. This subgroup did not differ significantly from the remaining 81 AS patients with respect to age, sex, NYHA class, medication, aortic valve area index, LV mass index or any measure of LV function (data not shown).

Plasma VIP was measured using commercially available radioimmunoassay kits (Immuno-Biological Laboratories, Hamburg, Germany). The method had a sensitivity of 3 pmol/l, an intra-assay variation of 3.9-4.1% and an inter-assay variation of 6.6-8.5%. NT-proBNP was determined using a commercial enzyme immunoassay (Biomedica, Vienna, Austria) with an intra-assay coefficient of variation of 8.5%. Endothelin-1 was measured as detailed previously [14]; the intra-assay coefficient of variation was 5.7%.

2.4. Statistical analysis
Comparisons across two or more groups were made with ANOVA for continuous variables and with the chi square test for frequency distributions. ANOVA with repeated measurements incorporating one grouping factor (control patients, patients with AS without HF, patients with AS and HF) and one within factor (aortic vs. coronary sinus measurements) was used to analyze the transcardiac gradients of plasma VIP, NT-proBNP and endothelin-1. Associations of VIP with the clinical characteristics and with the non-invasive and invasive cardiac measurements were studied using ANOVA and Pearson's correlation coefficients. The data are summarized as mean±S.E.M. unless indicated otherwise. p-values <0.05 were considered statistically significant. All analyses were done using commercial software (SYSTAT Version 9.1, Systat Inc.).


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 References
 
3.1. Characteristics of patients with and without HF
Forty-one of the 129 AS patients had HF. Patients with and without HF were of comparable age (70±2 vs. 68±1 year, p=NS) and had similar sex distribution (M/F, 19/22 vs. 45/43, p=NS). However, patients with HF had more severe AS (valve area, 0.33±0.02 cm2/m2 vs. 0.42±0.01 cm2/m2, p<0.001), higher LV mass (169±6 g/m2 vs. 143±4 g/m2, p<0.001), lower ejection fraction (52±2% vs. 64±1%, p<0.001), higher pulmonary wedge pressure (21±1 mm Hg vs. 9±1 mm Hg, p<0.001), shorter 6-min walking distance (235±18 m vs. 325±12 m, p<0.0001) and higher prevalence of atrial fibrillation (9/41 vs. 2/88, p<0.001). The prevalence of angiographically significant coronary artery disease was 40% in the presence of HF and 28% in its absence (p=NS).

Of the 41 patients with AS and HF, 25 had an LV ejection fraction ≥50% (mean, 62±1%) and thus, by our definition, diastolic HF. The remaining 16 patients had systolic HF with a mean ejection fraction of 36±2%. Patients with systolic HF had higher LV mass (184±7 g/m2 vs. 159±7 g/m2 in diastolic HF, p=0.020) but otherwise the characteristics of patients with the two subtypes of HF were not significantly different (age, sex, aortic valve area, pulmonary wedge pressure, 6-min walk, prevalence of atrial fibrillation, prevalence of coronary artery disease).

3.2. Systemic VIP concentrations in the presence and absence of HF
Plasma VIP averaged 20.0±1.3 pmol/l in the 11 patients free of structural heart disease, 21.1±0.5 pmol/l in the 88 AS patients without HF and 22.6±0.9 pmol/l in the 41 AS patients with HF (p=0.030). The type of HF did not make a difference: plasma VIP averaged 21.6±1.5 pmol/l in systolic HF and 23.3±1.2 pmol/l in patients with diastolic HF (p=0.390). VIP was also unrelated to age, sex, NYHA-class, 6-min walk, aortic valve area, LV mass, pulmonary wedge pressure and presence of coronary artery disease at angiography. Nor did VIP correlate with the systemic concentrations of NT-proBNP or endothelin-1.

3.3. Transcardiac gradients of VIP, NT-proBNP and endothelin-1
Fig. 1 shows plasma VIP concentrations in the aortic root and coronary sinus in the 11 control patients free of structural heart disease and in the subset of 48 AS patients in whom the coronary sinus was accessible for blood sampling, grouped by the presence and type of HF. ANOVA with repeated measurements showed a statistically significant difference across the groups (p<0.05) as well as a highly significant increase in plasma VIP from the aorta to the coronary sinus (p<0.00001). The transcardiac VIP gradient averaged +1.2±0.4 pmol/l in the control group (p=0.021 compared with zero), +1.2±0.2 pmol/l in 33 AS patients free of HF (p<0.001) and +0.8±0.3 pmol/l in 15 AS patients with HF (p=0.037). The differences across the group mean transcardiac gradients were not statistically significant as indicated by the lack of interaction between the grouping and within factors in ANOVA (see Fig. 1). The VIP gradient did not correlate with any clinical characteristic or any measurement of cardiac structure or function.


Figure 1
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  		Fig. 1 Concentration of vasoactive intestinal peptide (VIP) in the aortic root (open columns) and coronary sinus (CS, hatched columns) in the control group (no structural heart disease, n=11) and in the 48 patients with aortic stenosis in whom the coronary sinus was accessible for blood sampling, grouped according to the presence and type of heart failure. No heart failure (HF) (n=33), diastolic HF (n=8), systolic HF (n=7). The p-values are from repeated measurements' ANOVA. Due to the small numbers, patients with diastolic and systolic HF were considered as one HF group of 15 individuals in ANOVA.

 
Fig. 2 shows the concentrations of NT-proBNP and endothelin-1 in the aortic root and coronary sinus. The graphs demonstrate that both NT-proBNP (Fig. 2A) and endothelin-1 (Fig. 2B) were increased in patients with HF and that the heart released NT-proBNP and extracted endothelin-1 with the respective arterio-venous differences being widest in the failing hearts (see the p-values for interaction in Fig. 2A and B). The transcardiac VIP gradient showed no statistical association with the gradients of either NT-proBNP or endothelin-1.


Figure 2
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  		Fig. 2 Concentrations of NT-proBNP (A) and endothelin-1 (B) in the aortic root (open columns) and coronary sinus (CS, hatched columns). The formats and statistical analysis are identical to Fig. 1.

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
References
 
To study the role of VIP in HF, we measured concentrations of VIP in the aortic and coronary sinus in AS patients with and without HF. We found that VIP was elevated in HF, but only very marginally and without any relation to clinical or haemodynamic patient characteristics. The heart released VIP into the circulation but this was independent of whether the heart was structurally normal or diseased and failing. Thus, although VIP may be involved in the neural control of cardiac function, it is unlikely to have any major role in HF, at least when this is due to LV pressure overload.

Circulating VIP reflects overflow from nerve terminals in the splanchnic area and in the vascular walls [1]. VIP has a plasma half-life of about one minute [15] and a circadian rhythm peaking towards the evening hours [16,17]. Circulating VIP is not a direct measure of activity because the peptide can be released in tissues without an increase in its plasma concentration [15] and also because the VIP receptors may be altered in disease states [1,18]. Finally, altered metabolism of VIP in the liver, kidney and lungs may influence circulating VIP without any change in the nervous activity [1].

The biological actions of VIP- peripheral and coronary vasodilation with positive inotropy and chronotropy and cardioprotection during ischaemia—make it an attractive candidate as a compensatory mediator in HF. However, the data are inconclusive, while some studies have shown elevated plasma VIP in HF [6,7], others have not [8,9], and one study reported elevated VIP in mild but not in severe HF [10]. In our study, circulating VIP was marginally elevated in HF but had no relation to clinical, haemodynamic or echocardiographic patient characteristics. Admittedly, we studied patients with chronic HF due to LV pressure overload and the picture could be different in other types of HF by aetiology, stability or speed of onset. In acute myocardial infarction, plasma VIP rises by 30-60% during the first hours, declines below the normal level after the first day and recovers within 2 weeks [19,20].

We have shown for the first time that the heart releases VIP into the coronary circulation in man. VIP resides in the heart mainly in the vagal nerve fibers ramifying to the coronary arteries and veins, to the sinoatrial and atrioventricular nodes and to the atria and ventricles [1]. It is released by high-frequency vagal stimulation and by cholinergic and dopaminergic agonists, serotonin and prostaglandins. The step up of plasma VIP from the arterial to the venous side of the heart reflects spillover of the peptide released at the nerve terminals. This suggests that VIP-containing cardiac nerves are actively firing and participating in the regulation of coronary and/or myocardial function in man [21]. However, the quantity of VIP spillover depends not only on nervous activity but also on the function of the VIP-binding receptors in the heart. In HF, these are decreased in density but increased in affinity [18]. Previously, Smitherman et al. studying the effects of exogenous VIP in man found no difference between the aortic and coronary sinus VIP concentrations [22]. However, their patients were all men suffering from non-atherosclerotic chest pain which may have influenced the data.

The transcardiac gradients of NT-proBNP and endothelin-1 were determined here to validate our sampling procedure and to allow comparisons across the different endogenous vasoactive agents. The cardiac release and extraction of NT-proBNP and endothelin-1, respectively, accord with earlier observations [23,24] and were clearly more pronounced in the failing than non-failing hearts. The transcardiac VIP gradient, by contrast, was unrelated to the presence of HF and showed no correlation with the corresponding gradients of NT-proBNP or endothelin-1. These data also suggest that VIP is not important in HF.

A limitation of our work is that we did not measure the flow of blood in the coronary sinus. Therefore we could not determine the true quantity of VIP overflow from the heart (i.e. flowxarterio-venous concentration difference). Although this does not undermine our main findings-spillover of VIP from the heart and slight elevation of systemic VIP in HF-it may have influenced the between-group comparisons of the transcardiac concentration gradients. Since coronary flow is likely to be increased in LV hypertrophy, the mere arterio-venous concentration differences may underestimate the release and extraction of the vasoactive agents in patients with AS relative to the control group.

In conclusion, the present work shows that plasma VIP is marginally elevated in patients with HF due to AS and that both non-failing and failing hearts release VIP into the circulation. VIP may be involved in the neural control of cardiac function both in health and in disease but is unlikely to have a major counter regulatory role in HF, at least when this is due to LV pressure overload.


   Acknowledgements
 
We thank members of our staff, Drs. Markku Mäkijärvi, MD, and Hannu Parikka, MD, for collecting the blood samples in the control patients, and Liisa Blubaum, RN, for skilful assistance throughout this investigation. We also gratefully acknowledge the grants we received from (1) Sigrid Juselius Foundation, Helsinki, Finland; (2) Research Funds (EVO grant) of Helsinki University Central Hospital, Helsinki, Finland; and (3) Finnish Foundation for Cardiovascular Research, Helsinki, Finland.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 

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